Weighting Fault-Tolerant Multi-Record Answers in Amazon Route 53

Note

Records that use the multivalue answer routing policy behave in much the same way
as the configuration that is
documented in this tutorial. The main difference is that the tutorial configuration
lets you specify weights, which can be useful
when your endpoints have different capacities. For more information, see
Multivalue Answer Routing.

An Amazon Route 53 weighted record can only be associated with one record, meaning
a combination of
one name (for example, example.com) and one record type (for example, A). But it is often desirable to
weight DNS responses that contain multiple records.

For example, you might have eight Amazon EC2 instances or Elastic IP endpoints for
a service. If the clients of that service
support connection retries (as all common browsers do), then providing multiple
IP addresses in DNS responses
provides those clients with alternative endpoints in the event of the failure of
any particular endpoint.
You can even protect against the failure of an availability zone if you configure
responses to contain a mix of
IPs hosted in two or more availability zones.

Multi-record answers are also useful when a large number of clients (for example,
mobile web applications) share a
small set of DNS caches. In this case, multi-record answers allow clients to direct
requests to several endpoints
even if they receive a common DNS response from the shared cache.

These types of weighted multi-record answers can be achieved by using a combination
of records and
weighted alias records. You can group eight endpoints into two distinct record
sets containing
four IP addresses each:

endpoint-a.example.com, type A, with the following values:

192.0.2.1

192.0.2.2

192.0.2.128

192.0.2.129

endpoint-b.example.com, type A, with the following values:

192.0.2.3

192.0.2.4

192.0.2.130

192.0.2.131

You can then create a weighted alias record that points to each group: